This invention relates generally to landing gear used in the support of semitrailers and more particularly to gearing configurations of a landing gear.
Landing gear of the present invention has particular application in the support of semitrailers when they are not attached to a tractor. The landing gear conventionally includes a pair of telescoping legs capable of extending to engage the pavement or other supporting surface to hold up the front end of the semitrailer, and of retracting to move up out of the way when the semitrailer is being pulled over the road by a tractor. The extension and retraction is most often carried out by the driver manually turning a crank connected by gearing to a lead screw in the leg. The lead screw interconnects telescoping leg sections of the leg so as to retract a lower leg section into an upper leg section or extend the lower leg section from the upper leg section depending on the direction the screw is rotated.
The semitrailers are very large and heavy by themselves, and further carry large loads. In order to lift such loads when extending the legs, the gearing provides a mechanical advantage in addition to the crank. In providing the mechanical advantage, the rotation of the lead screw is very much retarded in relation to the rotation of the crank. In other words, it will require numerous turns of the crank to achieve a very small linear travel of the lower leg section relative to the upper leg section. The high ratio of turns per inch of travel is acceptable when the legs are actually bearing the load of the trailer because of the accompanying mechanical advantage. Once the load is relieved from the leg, such as when the semitrailer is supported by the tractor, the slow linear movement of the lower leg section becomes an issue because of the long time it takes to get the lower leg section retracted far enough above the ground for safe travel over the road. Likewise, slow extension of the lower leg section into engagement with the pavement is also highly undesirable. It is known to provide for shifting between a low gear and a high gear in the gearing, with the low gear providing the mechanical advantage needed for lifting large loads and high gear providing for more rapid linear movement of the lower leg section (i.e., a lower turns per inch ratio). Co-assigned U.S. Pat. No. 4,187,733 discloses gearing of this type. Generally, a large difference between the turns per inch ratio in low gear versus high gear is desirable.
One way to assist in providing greater lift in low gear is to provide a gear on an idler shaft located between the input shaft (of the crank) and the output shaft connected to the lead screw. This arrangement is typically referred to as a double reduction. An idler shaft requires additional space in the gear box, which is at a premium. In addition, there are two additional openings in the gear box containing bearings for the idler shaft. These openings provide an additional place from which leakage of lubricant becomes more likely over the life of the landing gear.
Conventionally, the gearing has been located in a gear box which is formed separately from the leg. For instance, the gear box may be formed from two halves which are individually stamped and later bolted together. The gears making up the gearing may be installed in one half of the gear box before it is completed. The gear box is welded or otherwise attached to the landing gear leg on the inside or outside of the leg. The input shaft from the crank, and the output shaft which is connected to the lead screw, are held by bearings located in the landing gear leg. The conventional construction requires a number of parts in addition to the landing gear leg and several manufacturing steps to assemble the gearing in the gear box with the input and output shafts and the leg. It is known to incorporate some of the gearing in the leg, but significant manufacturing steps are required to assemble component parts of the gearing together with the input and output shafts.